need advice about Monacor drivers

[steph_tsf]

hello, what Monacor drivers would you advise for :

- a 4th-order Bandpass (35 Hz to 120 Hz) (5" to 8" diameter)
- a Bass-Reflex box (120 Hz to 6 kHz) (3" to 5" diameter)

Thanks

[Inductor]

Hi Steph. The MONACOR SPH 130 seems to be the best mid. Of course you and others, will have to pay me a lot of cash for this information.

[Inductor]

I would also test/simulate the Monacor SPH-200KE (against the Monacor SPH-176) for the bass 4th-order Bandpass. Regards

[steph_tsf]

Here is Monacor SPH-200KE + SPH-130 combination simulated with LTspiceIV, including the active filters. See attached .zip.

[steph_tsf]

Here is Monacor SPH-265 + SPH-130 combination simulated with LTspiceIV, including the active filters. See attached .zip.

[Inductor]

It's an active xover right? You have the drivers in phase (0º phase/same phase) I suspect. Now if there is a difference like a relative offset between the woofer and the tweeter in which the AC of the woofer is located behind that of the tweeter, how do you deal with the phase alignments.

Note: In the case, a more complex, 4th-order Bandpass phase (does it matter or only for higher frequencies in this case for the tweeter).
(1. Time aligned, Phase coherent, Phase aligned, Transient accurate, What's up with that? - Kreskovs)
(2. The Evolution of JBL’s Large Format Monitor Loudspeaker - JBL)

[steph_tsf]

Originally Posted by Inductor

If there is a difference like a mechanical position offset between the woofer and the tweeter in which the AC of the woofer is located behind that of the tweeter, how do you deal with the phase alignments ?

Yes, that's absolutely true. If you put the tweeter on the same plane as the bass-midrange driver, then there is indeed a mechanical offset between the tweeter and the bass-midrange, as showed on the two pictures you have provided. Nowadays you can find loudspeaker simulation programs able to take this mechanical offset in account. They allow you to specify a mecanical offset. Then you see the disastrous consequences when summing up the tweeter and bass-midrange acoustic pressure. During the last 30 years I have played with complicated crossover fllters for blending the bass-medium with the tweeter. About 10 years ago I've discovered a better way to filter and blend the bass-medium with the tweeter. In order to use this improved method, you need a small size bass-medium driver "man designed" able to deliver a smooth acoustic response until 6 kHz or 8 kHz. When I say "man designed", I mean a transducer that got designed and optimized by a specialist, able to control the membrane break-up above 4 kHz. There are not many drivers like this on the market. Fortunately, the Monacor SPH-130 looks to be such "man designed" driver. For the treble range, you need a modern miniaturized dome tweeter like Visaton CP-13 (13 mm dome - limited to moderate listening levels) or Monacor DT-284 (28 mm dome - better suited to loud listening levels). You will then use a 1st order crossover filter : a coil for the SPH-130 (low pass), and a capacitor for the CP-13 or DT-284 (high pass). You put the crossover frequency at 6 kHz in case of a CP-13 or 4 kHz in case of a DT-284. This guarantees the complementary of the two signal branches, with a linear phase response when adding the two acoustic responses. Other solutons like 2nd order low pass filtering of the bass-medium may exist, but the tweeter high-pass becomes then alot more complicated than just a capacitor in series, for getting the complementary amplitude and phase response. Now you will ask : "yes, okay, let us go for a 1st order crossover filter, but how to compensate the mechanical misalignment ?". My answer is : "use a delay line in the tweeter". Such delay line is not complicated. The components values are not critical. Later on I'll do a simulation of such delay line if you want. If the mechanical misalignment is 35mm, the delay is 103µs with the sound speed equal to 340m/s. At 5 kHz, the sound wavelength is 68mm. Now you understand how a 35mm misalignment can ruin a crossover : this is equivalent to a 185 degree phase shift at 5 kHz ! If you don't put the delay line, you'll get a huge dip in the acoustic response. And if you invert the tweeter polarity, then you'll get a localized boost at 5 kHz preceded and followed by weird amplitude variations. Of course, you surely have realized that in the context basing on phase accuracy, it is mandatory to use a MTM arrangement : tweeter positionned in the middle, between the two bass-medium drivers. If you don't use a MTM arrangement, you'll never be able to attain the objective of phase accuracy.

Originally Posted by Inductor

It's an active xover right? You have the drivers in phase (0º phase/same phase) I suspect. In the case, a more complex, 4th-order Bandpass phase, does it matter or only for higher frequencies ?

The active crossover simulation around 100 Hz can be considered as accurate. At 100 Hz, the wavelenght is 3.4 meter. That's quite a lenght compared to an eventual subwoofer / bass-midrdange mechanical misalignment. Say the misalignment is 17 cm. This is equivalent to a 18 degree phase shift. That's quite neglectible. So yes, you will get a flat acoustic response from 40 Hz to 6 kHz with the combination that's simulated. But wait a moment. Look to the resulting phase response. Although the low frequency response is essentially flat between 40 Hz to 200 Hz, there is a -300 degree phase shift developing between 40 Hz and 200 Hz. Now you will ask me "How is this possible : flat amplitude but phase buildup ? Are you sure ?". My answer is "Yes, absolutely sure". You'll need some maths to figure out what's happening. But we can bypass this painful necessity. Let's act practical. If you want both a flat amplitude and a zero phase buildup, then you'll need a far more elaborate active crossover at 100 Hz. You'll need an electronic copycat circuit of the 2nd low pass subwoofer acoustic behaviour, kind of steep 2nd order lowpass at 100Hz. Actually, it is more complicated than this because in reality, it is the negative edge of a 4th bandpass filter. We may use 1 or 2 two opamps, so that's realizable. On top of this we need to add the crossover behaviour : a 2nd order lowpass at approx 250 Hz. This is one extra op-amp. So, with an electronic circuit containing 2 or 3 opamps, we can get an electronic image of the subwoofer low-pass acoustic response, when filtered. If you want to get a fully complementary crossover, all you need to do is to put a substractor. Take the input signal, and substract from it the anticipated subwoofer low-pass acoustic response, when filtered. At the end of such circuit, you get your beloved complementary high-pass signal. You'll discover that it has a slope of +6d/oct, like it was a 1st order high-pass, but with a added boost at the 100 Hz corner frequency. Oops : this is maybe too much for a Monacor SPH-130, because of limited excursion ... You may then think that the mission is completed, feeding the Monacor SPH-130 with this. Unfortunately, that's not the case. You'll need to reverse-equalize the SPH-130 acoustic response, making it appear like a perfectly flat driver from 50 Hz to 100 Hz, both in phase and amplitude, before actually feeding it with the beloved complementary high-pass signal. You'll need 1 or 2 more opamps for doing this empirically. This is the same kind of job as with the subwoofer, but now with an acoustic response inversion as target. And doing so you increase the excursion stress on the Monacor SPH-130 ... You may need an intelligent high-pass filter, with a variable corner frequency, for limiting the Monacor SPH-130 excursion in function of the deep bass content.

Then you realize what kind of electronic monster you are developing, and you may want doing the exact same in digital domain using minDSP or SynthMaker.
Regarding miniDSP we need to wait the release of a "free world IIRs + delays" plugin. "Free world IIRs" because as you may have noticed, the "bare hands" crossover filters we are designing here have nothing to do with Butterworth, Bessel and Linkwitz. "Delays" because a delay line is needed when dealing with the tweeter crossover. And I doubt miniDSP will ever be able to execute an intelligent high-pass filter, with a variable corner frequency, for limiting the Monacor SPH-130 excursion in function of the deep bass content.
Regarding SynthMaker, we need to wait the release of a Windows 7 Sound System -> VST bridge.

Want to do a practical workshop during this summer ?

[Inductor]

Originally Posted by steph_tsf

Want to do a practical workshop during this summer ?

What's that, where?
I'm not very much into active multiple systems, (but) more on passive components.

[steph_tsf]

Anywhere in Cascais. 33% of the time would be me and my wife at the beach, 33% eating and sleeping in a hotel, and 33% you and me designing, assembling and measuring some elaborate audio system. Need to find a decent hotel at a decent price in Cascais. Topics : measuring T/S drivers parameters using AudioTester3 (added mass method), simulating free air, closed box, bass reflex and 4th order bandpass speakers enclosures with LTspiceIV, simulating passive filters and multiway speakers enclosures with LTspiceIV, simulating active crossovers and multiway speakers enclosures with LTspiceIV. Aso with LTspiceIV : positive resistance drive, negative resistance drive, motional voltage extraction and feedback, acceleration piezo disc sensor and feedback.

[steph_tsf]

Here is Monacor SPH-250KE + SPH-130 combination simulated with LTspiceIV, including the active filters. See attached .zip.